This application claims the priority of French Application No. 98 01558, filed on Feb. 10, 1998.
The invention relates to a junction box for a tensioned cable, particularly an optical fibers cable.
The invention is applicable for making branch connections on line or in a section operated on cables.
In general, making a branch connection is an operation that consists of connecting one or several wires or one or several cable fibers to connect them to another cable.
The connection technique is a relatively recent technique used for optical fiber cables that consists of cutting the optical fiber(s) to be connected, to connect it or them to other fibers in another cable.
The applicant developed this technique with the development of Flexible Optical Networks (ROF). Refer to the diagram in FIG. 1 that illustrates the principle used for making branch connections to this type of network.
The invention can be better understood after a brief reminder about the development of the structure of currently available optical fibers.
The first cables specially designed for the production of inter-city networks are cables with grooved rods as illustrated in FIG. 2.
The cable with tubes technique was subsequently developed in order to better protect the fiber and also to encase it.
These tubes replace the grooves to more efficiently protect the fibers.
Their manufacturing process is better and less expensive than the grooved cable manufacturing process. These cables are illustrated in FIGS. 2A and 2B.
These cables were used for the production of connections between exchanges. The cables were connected at both ends and were usually used over long distances (city to city connections, creation of xe2x80x9cnationalxe2x80x9d networks).
A distribution approach was then considered for the production of networks in urban areas (ROFxe2x80x94flexible optical networks).
These looped networks, naturally protected by a return along a different route, improve reliability. For example, they were used for the connection of large cooperations (for example banks).
Business customers were connected more recently, usually in urban areas, with the use of the branch connection technique.
This provided an opportunity for the applicant to develop the branch connection technique.
Furthermore, two concepts of xe2x80x9csingle-tubexe2x80x9d or distribution cables with optical characteristics approximately the same as the characteristics of inter-city network cables were developed, but with a weight reduction (weight divided by 2 for the same diameter) and an increase in the number of fibers (4 to 5 times more fibers).
Unlike transmission cables, the structure of single-tube cables is characterized (in cables containing up to 288 fibers) by a thick high density polyethylene tube containing 2 or 4 carriers. These carriers stabilize the materials. In fact, they are made of a fiber glass composite or aramide wick. Laying is facilitated by their high tensile and compression strength.
Encasing of the fibers making up single-tube cables leads to two types of optical modules, namely ribbon fibers and fibers with flexible casings.
Ribbon fibers or flat cable fibers, as illustrated in FIG. 2C, are placed side by side in a polymerized casing. This encasing is done in the factory, and facilitates the earth connection.
Bulk fibers with flexible casings, frequently called micro-ducts, are illustrated in the sketch in FIG. 2D. These fibers are free to move within this colored casing. A combination of several casings is close to the state-of-the-art for a copper cable. Color marking identifies a module at the end, and also within the cross-section of a cable.
A branch connection is added into the network by using boxes designed for national networks.
Two types of boxes have been identified for this purpose:
A)xe2x80x94boxes in buckets or trays
B)xe2x80x94boxes with a base and a dome-shaped cover.
A: Boxes in buckets or trays are frequently prismatic. Cable crossings are laid out in opposition. When the cable passes continuously, an anchorage makes all cable carriers continuous. Therefore, there is one anchorage for each cable. These cables may enter on either side of the box through various sealed tubings or crossings. The cable crossing is in the same plane as the box joint plane. Therefore, the entire box has to be enclosed, usually using resins to make a good seal. Fibers are accessed by completely disassembling the box and opening the joint plane.
This box, designed for use in line with a cable over-length on each side, is more and more frequently used in a herring bone pattern, in other words in which all cables enter on the same side.
B: Boxes with base and a dome- or cap-shaped cover. They are characterized by a circular-shaped base on which rounded or oblong-shaped cable crossings cooperate with a heat sealed glued sleeve, to create the seal by deformation and by gluing.
This seal cannot be achieved unless the sleeve is put into position before the cable is installed and a heat source is necessary, which makes the operation difficult.
As in previous boxes, the anchorage transfers forces onto the cable carriers.
These boxes, widely used in England and America, are not suitable for integration of the anchorage inside the box.
Two other boxes have been described to facilitate branch connections to more recent cable structures:
C)xe2x80x94A box that was described in patent No. FR 96 07887 published under No. 2 750 222, and is characterized by its rounded shape. The cable over-length is wound around the perimeter, so that the connection can be made outside the pulling chamber. This box can be upgraded by the assembly of one or several bases.
The first disadvantage of box C is that it cannot be industrialized. It is designed for making branch connections on flexible cables that can be wound. The reduction in the anchorage volume and integration of the seal are useful but expensive, and furthermore space must be available for cavities to accommodate the anchorages.
D)xe2x80x94A box, also in the form of a tray like the previous description, comprises two symmetric elements. This box is interesting in that it is more compact, but also due to its mechanical seal. In practice it is a clone of box type A and has the same disadvantages. Mechanical continuity of the carriers is achieved by anchoring them.
A D type box derived from the design of the A type box has the same disadvantages, and particularly the same cumbersome anchorages, of the unjustified winding structures, since only a few fibers need to be organized in the case of a branch connection. The cable carrier structure is cut and reconstituted by anchorage in the box, which introduces long operations.
The winding area or the fiber access area does not facilitate connection ergonomy. In the case of a branch connection, it is desirable to have a length of at least 80 cm (40 cm on each side).
In summary, with existing boxes, the mechanical elements of the cables are cut and are then reconstituted. The anchorage operation generates large and expensive devices and introduces an increasing complexity in the design of boxes.
The box according to the invention overcomes these disadvantages.
With the box according to the invention, the cable protection can be reconstituted in the work area without the disadvantages of prior techniques, and in particular the integrity of the cable casing is maintained which immediately eliminates the need for anchorages.
The box according to the invention enables easy access to optical modules without management or organization of their over-length. With the invention, the continuity of the optical module is retained, together with a limited hierarchy of the branch connected fibers without any organization and management device.
The invention may be used in service ducts (vertical or horizontal cableways) considering the small cross-section of this box, the center line of which is coincident with the center line of the cable.
Unlike boxes according to prior art, this box may be used to repair a distribution cable (single-tube) while it is buried in the ground after an incident, for example an accidental break to the cable by mechanical machinery.
Branch connected cables inserted axially inside seals made of industrial products can reduce the cost of these crossings.
This box facilitates access to the fiber in all pulling chambers through which a distribution cable passes.
Access points no longer require expensive over-lengths.
The box facilitates branch connections during installation while the network is being built, and later even if the cable has been laid, regardless of the type of the pulling chamber.
The box is suitable for above-underground environments (columns, building foundations, etc.) or overhead environments (top of posts, building facades).
Therefore, one of the main purposes of the invention is a junction box for a cable, and particularly a single-tube optical fiber cable for the connection of one or several wire(s) or fiber(s) of this cable, called the connected cable, to one or several wires forming at least one other cable called the connecting cable, characterized particularly in that it comprises a hollow support suitable for a tensioned connected cable crossing, a spacer to hold the casing of the said axially cut cable, spread inside the hollow support in order to thus free the cable wires or fibers.
According to another characteristic, the hollow support comprises several successive compartments to house over-lengths of wires or fibers of connecting cables.
Preferably, the spacer is formed of two parallel rods rigidly attached to box attachment washers.
The hollow support is formed by a generally parallelepiped-shaped base in which there is a channel with dimensions suitable for holding the connected cable with the spacer.
The box includes one or several splice support plates located above and along this channel.
The base is closed by a cover and a gasket placed between this cover and the base that seals the box. The longitudinal edges of the base have a corrugated shape corresponding to the shapes of the compartments in order to contain the clips so that the cover can exert a pressure on the said gasket.